Angel from Presepio

[During the Mass] “At such a time angels stand by the Priest; and the whole sanctuary, and the space round about the altar, is filled with the powers of heaven, in honor of Him who lies thereon.”
John Chrysostom – On the Priesthood – http://www.newadvent.org/fathers/19226.htm

This may be a closer translation of the quotation you often see as: “When the Mass is being celebrated, the sanctuary is filled with countless angels, who adore the Divine Victim immolated on the altar.”